Chemistry NCERT Exemplar Solutions Class 12th Chapter One

Determining empirical formula of the given compound.

$\mathrm{\%}ofC=\frac{48.5}{116}*100\mathrm{\%}=41.8\mathrm{\%}$               

$\mathrm{\%}ofH=\frac{7.5}{116}*100\mathrm{\%}=6.5\mathrm{\%}$               

$\mathrm{\%}ofO=\frac{60}{116}*100\mathrm{\%}=51.7\mathrm{\%}$               

              Mass         Moles                  Simplest ratio

C            41.8g        $\frac{41.8}{12}=3.48$         $\frac{3.48}{3.23}\approx 1$                 

H            6.5 g        $\frac{6.5}{1}=6.5$             $\frac{6.5}{3.23}\approx 2$                      

O           51.7 g        $\frac{51.7}{16}=3.23$         $\frac{3.23}{3.23}=1$                  

Ratio of moles of C, H and O is 1 : 2 : 1

A. CH₃COOH ⇒ C : H : O = 2 : 4 : 2 = 1 : 2 : 1

B. HCHO ⇒ C : H : O = 1 : 2 : 1

C. CH₃OOCH₃ ⇒ C : H : O = 2 : 6 : 2 = 1 : 3 : 1

D. CH₃CHO ⇒ C : H : O = 2 : 4 : 1

So, CH₃COOH and HCHO formulae agree with the given data

74. Option (ii) Assertion and reason both are correct statements, but reason is not correct explanation for assertion is the answer since in graphite carbon atoms are arranged in different layers and each atom is covalently bonded to three of its neighbouring atoms in the same layer due to which the fourth valence electron of each atom, present between the different layers is free to move and this makes graphite a good conductor of electricity.

As different layers can slide over each other which makes it soft. while in case of diamond C atom is bonded covalently with their adjacent atoms throughout the crystal. Thus, all the four valencies are satisfied. Covalent bonds are strong and directional in nature ; therefore, atoms are held very strongly at their positions. This is why diamond is hard and has a very high melting point but decomposes before melting, also acting as an insulator.